Modeling the Effects of Fly Ash Characteristics and Mixture Proportions on Strength and Durability of Concretes
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MODELING THE EFFECTS OF FLY ASH CHARACTERISTICS AND MIXTURE PROPORTIONS ON STRENGTH AND DURABILITY OF CONCRETES ELIZABETH L. WHITEa'b, DELLA M. ROYc, and PHILIP D. CADYa Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802 a. also affiliated with the Department of Civil Engineering b. also affiliated with Environmental Resources Research Institute c. also affiliated with the Department of Materials Science and Engineering Received 10 November,
1986; refereed
ABSTRACT Factor analyses and cluster analyses were the modeling tools used to relate the chemical and physical characteristics of fly ash and cement to the strength, sulfate resistance, and freeze-thaw durability of fly ash-modified concrete. A Type I Portland cement was mixed with base load and upset load condition fly ashes from three different power plants in each of five regions in the United States. Based on the interactions between the reactive constittuents of the cement and fly ash, common factor loadings were identified. Cement loaded onto the early strength factor; fly ash loaded onto the later strength factor. In some subgroups the quantity of mixing liquid loaded separately as representative of the high water/cement ratio, which masked the reactive interactions between the fly ash and cement. In other subgroups the inter-relationships between sulfate resistance and strength with fly ash/cemment fineness, CaO content, and alkali content were represented in the factor analysis as well as in the numerical analysis models. INTRODUCTION To assess the performance (strength, sulfate resistance, and durability characteristics) of fly ash in concrete, both a factor analysis model and a cluster analysis model were proposed (Fig. 1) to specifically address the chemical and physical properties of the fly ash and cement [1]. Fly ashes were collected during base load and upset operating conditions from 16 plants within five different regions in the United States. During base load and upset conditions the coal source was constant, except for one case where the clay (partings) content and composition of the coal source controlled the fly ash properties and thus the properties of the resultant fly ash/concrete. These ashes were used for preparing three sets of concrete mixture formulations in which several factors were varied. Mixtures were formulated with (a) no additives, (b) a water reducer, and (c) a water reducer and an air entraining agent. Within each of the above subsets, comparisons were made at a second level between each pure cement concrete mixture at 404, 351, 297 and 3 244 kg per cubic meter of cement (kg/m ) ( = 680, 590, 500 and 410 lbs of 3 3 cement per cubic yard (lbs/yd )). At a third level, the 351 kg/m pure cement concrete mixtures were compared with a 15 weight percent (wt.%) mixture of 53 kg (90 lbs) of fly ash with 297 kg (500 lbs) of cement, and a 30 wt.% mixture of 107 kg (180 lbs) of fly ash with 243 kg (410 lbs) of cement. One hundred and seventy-seven separate mixtures were investigated. Fly ash i
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